The vocal and dance group known as Unique -- Emone Jones, 16, Darchae Kelsey, 15, and Jameise Fox, 14 -- walked onto the stage at McKinley Technology High School to perform, and a crowd of nearly 700 whooped. After more than 20 hours of practice, Unique's chance to top the other acts hinged on this moment.

Emone, the singer and a 10th-grader at McKinley, waited for the soft strains of the Mariah Carey ballad "Hero" to start. But the silence stretched on. A song came on, the wrong one. More silence. Then another wrong song.

Finally, Emone squared her shoulders and lifted the microphone. "We'll just do this a cappella," she said. With the poise of a professional, Emone crooned the low notes and belted out the high ones as the dancers moved, garnering applause that brought a wide smile to her face.

Despite a missed song cue here and a faulty microphone there, a citywide talent show, a joint effort between the mayor's office and nonprofit groups, brought unbridled joy Thursday night to an audience of giddy teenagers, with and without chaperones.

The show's theme was SOUL -- Saving Our Children's Lives -- and it was planned as a tribute and antidote to the gun violence that has killed 21 people younger than 18 this year -- an inexplicable surge of violence as overall crime in the city has fallen. In his opening remarks, Mayor Anthony A. Williams (D) called for a moment of silence and echoed the frustrated refrain heard from the pulpits at child funerals this year.

"I am tired of losing the contributions, the ideas, the dreams and the self-expression of young people," the mayor said. "Tonight is a demonstration of what we can do as a community."

During the performances, high school students from across the city loudly cheered their friends and danced with the acts. Families sang out loud and to each other.

"This is about having a good time," said Keisha White, 14, a McKinley ninth-grader.

The producer of the talent show was Atif Tate, the founder of Music Future, a nonprofit group that offers after-school music composition and production classes. Tate had just two weeks to pull everything together.

"We have to reach out to kids who have these music dreams and remain positive," Tate said.

The vibe was so feel-good that organizers did not require everyone to pay the $10 admission. The money collected, about $1,000, is designated to help the competition's winner produce a professional-quality song. The winner's song is to be submitted to the management and record company of R&B group New Edition, which judged the contest.

New Edition, which has performed for more than 20 years, also spoke at three city schools Thursday. The singers acknowledged that their one-day appearance was fleeting, but they came to the District after telling the mayor in August that they wanted to be more involved in community issues.

"We're just trying to start a domino effect," said singer Ralph Tresvant, 36.

Competition among the performers was jovial.

Rapper Marcus Waddy, 14, who goes by Lil' Mick on stage, got up at 5 a.m. Thursday to practice the rap lyrics of his song "Baby Girl" in the bathroom mirror. For his moment on stage, he chose a red designer T-shirt, a gray zippered and hooded sweat shirt and jeans. The outfit hung baggy on his frame.

"I just feel like it's my time to shine," said Marcus, who added that he has wanted to be a rapper since he was 5.

The singing duet Passion -- Keisha Rayfield and her friend Crystal Timus, both 15 and 10th-graders at McKinley, had practiced all week hitting the high notes of the Mariah Carey ballad "Never Too Far."

Crystal said she was excited about the talent show because for most activities in the city, "you have to be 18 and older" to participate.

Keisha's mother, Vicky Rayfield, said the two girls have been singing together since junior high school. Music was a safe way to keep her daughter and other teenagers involved and engaged in positive pursuits.

"If we put the arts back in the schools, it gives them more to do than being out in the streets," Rayfield said.

Two hours into the show, things were going into overtime. Talent coordinator Takiyah Tate, founder of Still I Rise Inc., an arts company, tried to contain the backstage chaos and reassure the children, some of whom were near tears, that they would be able to perform.

And, in the end, everyone did. And when the winners were announced, DC Dragons Dancarate, a spirited grade school trio, and singer Robyn Norris, many of the participants left on an upbeat note, despite not winning anything.

Crystal and Keisha accepted congratulations and hugs from friends after the show.

"My momma's planning to pay for us to go to the studio," Crystal told them. "We're going to do our demo."

Emone Jones, center, practices dance steps at McKinley Technology High School as Keisha Rayfield, far left, and Crystal Timus watch. At right is Jameise Fox, and rapper Marcus "Lil' Mick" Waddy is in back.